Knights of Sidonia (シドニアの騎士, Shidonia no Kishi) is a mechamanga series by Tsutomu Nihei, serialized by Kodansha in their magazine Afternoon between April 2009 and September 2015, localized in English by Vertical. An anime television series adaptation, produced by Polygon Pictures, aired between April and June 2014 and a second season aired between April and June 2015. A second season of the series, Knights of Sidonia: Battle for Planet Nine (シドニアの騎士 第九惑星戦役, Sidonia no Kishi: Daikyuu Wakusei Seneki), aired between April 11, 2015 and June 27, 2015. The localized series is available for streaming exclusively on Netflix in all its territories as part of its original programming.

The story follows humans as they struggle to survive against the threat of the shapeshifting gigantic alien monsters called Gauna (奇居子). The manga begins a thousand years after humans flee from Earth, which was supposedly destroyed by the Gauna, aboard massive spaceships created from the remains of the planet. The Gauna follow the emigration ships into space, forcing the humans to create large mechanized weapons called Guardians (衛人 Morito) to protect themselves. Most people in the surviving human population are screened and drafted as Guardian pilots at a young age, if they are shown to be capable of piloting the mecha. The story focuses on one of such ships named Sidonia which has developed its own human culture closely based on that of Japan where human cloning, asexual reproduction and human engineering such as controlled hybrid human/animal mutations and human photosynthesis are commonplace.